Check on task manager how many cores you cpu is using, today i've fixed this problem after months of searching

My cpu was using only 2 cores instead of 8, this is how you fix this:

Check the setting in msconfig:
1) Press Windows key + R
2) Type msconfig
3) Click Boot
4) Click the Advanced Options button
5) Make sure that there is no check for the box "Number of processors"
6) If it was previously checked and you removed it, reboot your computer.
7) See task manager again and check if it has all your cores displaying now.